The strength-endurance relationship in skeletal muscle: its application to helmet design.

The isometric strength and endurance of the neck muscles in man was measured in four male subjects during dorsal, ventral, and lateral flexion of the head in a helmet dynamometer. The purpose of these experiments was to quantify the maximum strength of the neck muscles in these directions and to examine the relationship between isometric strength and endurance for various submaximal isometric tensions. Isometric contractions were sustained to fatigue by these subjects at tensions of 25, 40, 55, 70, and 90% of the maximum isometric strength in each of the directions of movement. Generally, the endurance of the muscles involved in ventral flexion was less than that found in dorsal and lateral flexion of the head. However, the strength of the muscles involved was progressively greater for lateral, dorsal, and ventral flexion, respectively. The implication of these findings in helmet design and helmet loading are discussed.